1. Field of the Invention
The present invention relates to CMOS integrated circuits. In particular, the present invention relates to a CMOS output buffer circuit.
2. Description of the Prior Art
Digital logic, in the form of integrated circuits, has found wide spread use in virtually every type of electronic system. The interface function is a basic function of any electronic system--it allows the logic of one integrated circuit device to interface with other devices. One important component for this interface function is the output buffer which, when enabled, provides an output which is a function of data received from other logic circuitry of the integrated circuit.
CMOS output buffers typically use a P-channel pull-up FET and a N-channel pull-down FET connected to the output terminal. Depending upon the state of the data signal input and an enable signal, either the P-channel FET or the N-channel FET is turned on.
In general, the prior art CMOS output buffers have not been capable of providing output drive current of the magnitude possible with bipolar integrated circuits (for example TTL circuitry). Attempts to achieve higher output drive currents from CMOS output buffers have resulted in sacrifices in speed and output signal distortion due to internal chip ground bounce or output signal ringing.